Post-Mortems: a useful – sometimes vital - diagnostic tool

A post-mortem can be a useful – sometimes vital - tool to diagnose the cause of a health problem on the farm. It will cost money to carry out, but will save money in the long term if it can identify the specific disease issue, thereby enabling a more targeted approach to treatment and prevention.  For best results, the fresher the carcase the better, and/or consider sacrificing one of the sick animals.

Differentiating diseases

A post-mortem can be of great value, not just in determining what that one animal died of, but also because it may identify a disease issue which is sub-clinically affecting the whole flock or herd.

A lot of diseases cannot be diagnosed purely on clinical signs. Liver fluke, for instance, can have various signs, which may be missed or confused for other problems.

For example, chronic weight loss in sheep can be caused by fluke, but also by several other diseases which are hard to diagnose. Some have severe consequences. Without a post-mortem it is very difficult to differentiate fluke from OPA (a contagious tumour of the lungs) or Johne’s disease. Fluke is easily treated and prevention is not difficult. However undiagnosed OPA is a contagious disease, which can be devastating if left to run its course.

If lambs are scouring, then post-mortems can be very useful in determining which treatment to administer. Money spent on coccidiosis treatment will have been wasted if lambs have actually got Nematodirus. For the cost of a post-mortem, you are avoiding wasting time and money on the wrong treatment.

Pneumonia in calves is another example. Do you know why your calves are dying? Pneumonia does more than cause coughing in the shed. Diseased calves can be found dead, and more can follow if the cause is not known and treated appropriately. Samples taken from post-mortems can confirm what caused the pneumonia and allow appropriate vaccination, antibiotic treatment or other preventative measures to be instigated.

Getting results from post mortems

With some diseases, such as liver fluke, post-mortems can allow a diagnosis on the spot, but others may require tissue samples to be sent off for further tests.

It can be frustrating when a post-mortem does not provide any answers, so to increase your chances of success, take care when choosing which dead animal to take for testing. An animal’s body starts decomposing as soon as it dies - the guts start to decompose within 20 minutes of death. So, the longer it’s been dead the less useful it is.

An animal that has been dead for 36 hours will be of limited use, although some information can still be gleaned at this stage. But if an animal has been dead for three days in July, then it is not worth post-morteming!

So the rule of thumb is ‘the fresher, the better’. In fact, if there is a sick animal still alive, but near death, then it might be worth sacrificing it to maximise the chances of getting a useful outcome from the post-mortem.

Ask your vet for advice about this, and choose a sick animal which best represents the problem you are having. For example, in a case of pneumonia in calves, pick one with showing signs which are most like the ones that have already died, and not the calf which has been scouring, when the others did not.